Whole-field determination of isoclinic parameter by five-step color phase shifting and its error analysis

Combining color imaging with phase shifting, a technique named five-step color phase shifting is presented to determine the whole-field isoclinic parameter. Relevant theory is derived and explicit conditions for directly determining the isoclinic parameter in the range of [0,π/2] are given. The unloaded light intensity of the model is systematically studied. A color camera recorded five isoclinic images coupled with isochromatics from a plane polariscope with five different settings, respectively. Experiments have been carried out with a circular disk under diametral compression and errors have been analyzed and estimated. This technique utilizes white light, which avoids undefined isoclinics near the locations where the isochromatics exist and will have active effect on experimental stress analysis and structural strength design.     

光弹等差线与等倾线参数的全场检测法

本文研究了一种自动获得全场等差线级数与等倾线参数角的方法.该方法是根据“相移”思想,利用数字图像处理技术,对光弹等差线图与等倾线图进行位相检测,经过去包裹处理,确定出全场各点的等差条纹级次与主应力方向角.最后通过典型实验,考核了这种方法的正确性与处理精度。     

A numerical comparison of real-time phase-shifting algorithms

Among data acquisition techniques in digital photoelasticity, the integrated phase shifting technique (IPST) can real-time analyze the photoelastic parameters at a video rate of the high speed CCD camera. In this paper, fourteen algorithms are described by different configurations of the rotating an analyzer at a constant rate and an output quarter-wave plate at another constant rate. The theoretical comparisons of the algorithms are given by the simulated phase distributions of the isochromatic and isoclinic parameters of the disk under two cases that the load keeps unchangeable or linear increasing in exposure time of the camera. Then a guideline is given to alleviate the influence of the load changing with time on the IPST.     

Determination of isoclinics in photoelasticity with a fast regularized estimator

The determination of isoclinics from photoelastic fringe patterns is a key problem in photoelasticity. Dealing with this problem, however, is not a simple task when isotropic points are present which is common for most experimental situations. Because of this, few researchers have proposed effective and practical solutions. Visualizing this problem as the problem of the determination of the modulo 2π fringe orientation, in this paper it is proposed an efficient regularized algorithm to solve it. Experimental results show that the proposal is effective and can be used with either monochromatic or white light.     

Phase-Stepping Photoelasticity by Use of Retarders with Arbitrary Retardation

The present paper describes a new phase-stepping algorithm for the analysis of isochromatics and isoclinics using retarders with arbitrary retardation. A retarder used in the proposed method is not necessarily a quarter-wave plate specified for the wavelength of the light used. Not only the isochromatic and isoclinic parameters but also the retardation of the input and output retarders are determined simultaneously by the proposed phase-stepping method. Thus, accurate analysis can be performed by the proposed method even if accurate quarter-wave plates are not used. In addition, any wavelength of visible light can be used in a single polariscope without requiring matching the wavelength of the quarter-wave plate. Thus, a multi-wavelength technique is easily combined with the proposed method for accuracy improvement, phase-unwrapping, or correction of ambiguity.     

Numerical analysis of phase-stepping interferometric photoelasticity for plane stress separation

A phase-stepping method for interferometric photoelasticity is proposed to determinate whole-field plane stress components. Isopachic phase can be obtained by rotating polarizer, second quarter-wave plate and analyzer at definite optical arrangements. On the other hand, isochromatic and isoclinic phases can be determined in a circular polariscope arrangement. Furthermore, a load-stepping method is adopted to overcome the wrong mathematic sign of the isochromatics in the ambiguity regions and the influence of initial interferometric fringes on the isopachics. Light intensities and phase-stepping formula for the proposed method are derived using Jones calculus. Simulation of a circular disk under diametral compression demonstrates the feasibility of the proposed method.